1. Field of the Invention
The present invention relates to a high-voltage capacitor manufacturing method and to a high-voltage capacitor appropriate for use in an ambient gas of a gas laser device.
2. Description of the Prior Art
There has been conventionally used a high-voltage capacitor as shown in FIG. 8 for the purpose of exciting an electric discharge in a high-voltage carbon dioxide gas laser, an excimer laser, or the like. The high-voltage capacitor 17 is provided with electrodes 2 formed on both end surfaces of a capacitor element 1 made of a dielectric ceramic and external terminals 3 connected respectively to the electrodes 2. The high-voltage capacitor. 17 has an insulating protection structure achieved by covering the entire periphery of the body of the capacitor except for the outer end portions of the external terminals 3 with an insulating protection material 15 made of a mold resin such as epoxy based resin.
The high-voltage capacitor is generally used in the atmosphere, however, in an excimer laser, there has been a growing trend of placing the high-voltage capacitor in a laser chamber filled with a laser medium gas composed principally of XeCl or KrF in order achieve an improved oscillation efficiency.
However, in the conventional high-voltage capacitor 17, a highly corrosive halogen gas such as Cl.sub.2 and F.sub.2 generated in the laser medium gas reacts with the insulating protection material 15, resulting in deterioration of the laser medium gas which serves as an ambient gas and deterioration of the insulation property of the insulating protection material 15. As a countermeasure for the aforementioned problem, the present inventor has proposed a high-voltage capacitor as disclosed in Japanese Utility Model Laid-Open publication No. HEI 03-34957. Referring to FIG. 9, a high-voltage capacitor 18 is formed by enclosing the periphery of a capacitor body 5c with a casing 6 made of a material such as fluororesin or alumina ceramic having a high corrosion resistance, filling an internal space with an insulating protection material 15 made of a mold resin such as epoxy resin, and leading external terminals 3 to the outside of the casing 6.
In injecting a mold resin such as epoxy based resin to fill the internal space with the resin, there may be an incomplete filling performance such as generation bubbles in the resin, leakage of the resin out of the casing, and generation of an unfilled portion in the casing. Therefore, when the laser chamber is internally evacuated with the high-voltage capacitor 18 placed in the laser chamber and thereafter the pressure inside the chamber is increased to provide a halogen gas environment, there has been such a problem that the electric characteristic of the high-voltage capacitor 18 abruptly deteriorates due to a possible occurrence of a phenomenon in which the halogen gas intrudes into the casing 6 of the high-voltage capacitor 18 or corrodes the resin leaking out of the casing 6, and a phenomenon in which a gas or powdery dust is generated simultaneously with the corrosion, resulting in contaminating the laser medium gas and degrading the life span of the laser device.
Furthermore, the excimer laser device is a sort of pulse gas laser in which an electric discharge repetitively occurs in the ambient gas to achieve laser oscillation. Therefore, the high-voltage capacitor is used in a severe condition in which the capacitor is exposed to the halogen gas as well as ultraviolet rays and discharge plasma due to the electric discharge. However, the conventional high-voltage capacitor has put only the reaction thereof with the halogen gas into question, and has not taken into account the deterioration caused by ultraviolet rays and discharge plasma due to the electric discharge. Accordingly, there have been problems as follows in realizing practical usage of the capacitor.
(1) The material covering the capacitor body is selected by its anti-halogen gas characteristic, and therefore, a concern arises in that the material may be deteriorated by the ultraviolet rays and discharge plasma generated due to the electric discharge depending on the material.
Particularly, when the exterior surface of the material covering the capacitor body is decomposed by the discharge plasma, the decomposed material scatters in a form of gas or powdery dust, resulting in contaminating the ambient gas and deteriorating the efficiency and life span of the laser device.
(2) A portion covering the capacitor body has no sealing portion, and therefore, a concern arises in that the ambient gas may enter into the hermetic casing during use.
When the ambient gas enters into the hermetic casing, the gas reacts with the insulating protection section to degrade the insulating property, which possibly degrades the dielectric performance or contaminates the ambient gas due to the generation of gas and powdery dust in company with the reaction, resulting in a problem of reducing the life span of the laser device and so forth.
(3) The electrode terminals are made of a material such as copper or brass. This causes a problem in that the electrode material may react with the halogen gas or the ultraviolet rays or discharge plasma generated due to the electric discharge, resulting in contaminating the ambient gas environment.